Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) are the major semiconductor devices in Integrate Circuits (ICs), especially in Ultra-Large-Scale Integrations (ULSIs). With the rapid development of the fabrication techniques of ICs, the technical node of the semiconductor technology has continuously decreased; and the feature size of the semiconductor devices follows the Moore's law. When the size of the semiconductor devices shrinks to a certain scale, secondary effects also continuously emerge because of various physical limitations; and it may be more and more difficult to reduce the feature size of the semiconductor devices according to a certain ratio. For example, in the field of semiconductor manufacturing, how to solve the large leakage current issue of the semiconductor devices is one of the current major challenges when reducing the size of the semiconductor devices.
The large leakage current issue of the semiconductor devices is caused by the continuous shrinking of the thickness of the traditional gate dielectric layer made of silicon oxide. One of the solutions is to substitute the traditional silicon oxide gate dielectric layer with a high dielectric constant (high-K) material. Further, a metal material is used as the gate electrode material to avoid the Fermi-level pinning effect and the boron penetration happing between the high-K gate dielectric layer and the traditional gate electrode material. Such a gate structure may be referred as a high-K metal gate (HKMG) structure.
Although the introduction of high-K dielectric material and the metal gate material is able to reduce the leakage current of the semiconductor devices to a certain extent, the electrical properties and the reliability of the semiconductor devices need further improvements. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.